MODELING OF PLASMA-ETCH PROCESSES USING WELL STIRRED REACTOR APPROXIMATIONS AND INCLUDING COMPLEX GAS-PHASE AND SURFACE-REACTIONS

A 0-D or well stirred reactor model determines spatially and time-aver aged species composition in plasma-etch reactors, through solution of species, mass, and electron-energy balance equations. The use of well stirred reactor approximations reduces the computational expense of de tailed kinetics calculations and allows investigation of the dependenc e of plasma chemistry on etch-process parameters. The reactor is chara cterized by a chamber volume, surface area, net mass flow or residence time, pressure, energy loss to surroundings, power deposition, and in let-gas composition. The electron-energy equation includes a detailed power balance with losses to ions and electrons through the sheath, as well as inelastic and elastic collision losses. The model employs rea ction rate coefficients for electron-impact reactions, which require a n assumption of the electron energy distribution function (EEDF). We c ompare model results using Maxwellian EEDF's, as well as reaction-rate coefficients determined as a function of average electron energy thro ugh solution of the Boltzmann equation, for chlorine chemistry. The Bo ltzmann rates are determined by time-lagging the equilibration of elec trons with applied electric fields. The Maxwellian reaction rates give higher ionization fractions than the Boltzmann rates, affecting the p redicted electronegativity and positive ion composition for chlorine p lasmas. The model also shows a strong sensitivity of the plasma compos ition to the assumed surface-recombination probability of atomic chlor ine.